Electrochromic display device, fabrication method therefor, and driving method therefor

ABSTRACT

An electrochromic display device includes a display substrate, a counter substrate facing the display substrate, counter electrodes formed on the counter substrate, at least first and second display electrodes arranged between the display substrate and the counter electrodes, the first display electrode and the second display electrode having a predetermined distance from each other, a first electrochromic layer arranged on the first display electrode and a second electrochromic layer arranged on the second display electrode, an electrolyte layer arranged between the respective first and the second display electrodes and the counter electrodes, and a protective layer made of an insulator material formed on a counter electrode facing side surface of one of the first and the second display electrodes such that the protective layer is sandwiched between the selected one of the first and the second display electrodes and a corresponding one of the first and the second electrochromic layers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The disclosures herein relate to an electrochromic display device, amethod for manufacturing the electrochromic display device, and a methodfor driving the electrochromic display device, and more specificallyrelated to an electrochromic display device capable of independentlydisplaying multicolor, a method for manufacturing such an electrochromicdisplay device, and a method for driving such an electrochromic displaydevice.

2. Description of the Related Art

Electronic paper has been increasingly developed as electronic mediareplacing ordinary paper. The feature of the electronic paper may bethat its display device is handled as ordinary paper, which differslargely from related art display devices such as cathode ray tubes orliquid crystal display devices. For example, the electronic paper may bea highly reflective display device capable of exhibiting high whitestate reflectance and high contrast ratio, high definition, stablememory effects, low-voltage driven, thin and lightweight, andinexpensive characteristics.

Various types of display devices have been proposed suitable for theelectronic paper. Examples include a reflective liquid crystal displaydevice, an electrophoretic display device, and a toner electrophoreticdisplay device. These types of display devices may be provided withlayers of different color filters so as to display device multiplecolor. However, the color filters themselves may absorb light to lowerthe reflectance of the display device. Thus, the above types of displaydevices may have difficulty in producing multicolor images whilemaintaining certain white state reflectance and contrast ratio.

Meanwhile, as an example of a reflective display device without havingcolor filters, an electrochromic display device may be given. Theelectrochromic display device utilizes electrochromism. Theelectrochromism is a phenomenon in display devices of materials thatexhibit reversible color changes induced by the application of voltages.When a voltage is applied to the electrochromic display device,electrochromic materials undego reversible redox reactions to reversiblychange color. The electrochromic display device is a reflective displaydevice, has memory effects, and capable of being driven by a lowvoltage. Accordingly, the electrochromic display device has beenextensively studied as one of the prospective candidates for theelectronic paper display devices, from material development to devicedesign.

Note that the technology of the electrochromic display device is basedon the principles of redox reactions to develop or dissipate colors ofmaterials. Accordingly, electrochromic responsiveness may be relativelylow. For example, Japanese Patent Application Publication No.2001-510590 (Patent Document 1) discloses an example of anelectrochromic system utilizing the above principles of redox reactions.In this electrochromic system, electrochromic compounds are fixed nearelectrodes such that the system has a very rapid electrochromic effect.In the system disclosed in Patent Document 1, electrochromic responsetime was significantly improved from about ten seconds typicallyobtained in the related art electrochromic display devices to onesecond.

Further, since the electrochromism is an electrochemical phenomenon,electrochromic responsiveness or memory effects of color in theelectrochromic display device may be largely affected by the performanceof the electrolyte layer (e.g., ionic conductance) forming theelectrochromic display device. The electrochromic display deviceincluding the liquid electrolyte layer formed by dissolving electrolytesinto solvents may exhibit excellent electrochromic responsiveness;however, the electrochromic display device may exhibit inferior elementstrength or reliability.

However, a solid-state electrolyte layer or a gel-like electrolyte layerhas been proposed to overcome such inferiorities. Specifically, thesolid-state electrolyte layer formed of polymeric solid-stateelectrolyte has been proposed. The electrical conductivity of thepolymeric solid-state electrolyte may be approximately 3 digits lowerthan an ordinary nonaqueous electrolytic solution. To overcome such lowconductivity of the polymeric solid-state electrolyte, Japanese PatentApplication Publication No. 63-94501 (Patent Document 2), for example,proposes a semisolid electrolyte layer obtained by dissolving polymersinto an organic electrolytic solution, or an electrolyte layer havingcross-linked polymers obtained by allowing electrolyte-containing liquidpolymers to undergo polymerization reaction.

However, in the electrochromic display device formed of pixel electrodesarranged in a matrix and configured to display or dissipate desiredpixels, electric charges are likely to diffuse outside of the selectedpixel regions within the electrolyte layer. In particular, if theelectrolyte layer is a liquid electrolyte layer, electric charges aremore likely to diffuse outside of the selected pixel regions. Toovercome such charge diffusion in the electrolyte layer, Japanese PatentApplication Publication No. 2008-304906 (Patent Document 3) proposes adisplay device capable of selectively displaying desired pixels alone.In this display device, the electrolyte layer is formed corresponding tothe selected pixels to be displayed to prevent the electric charges fromdiffusing outside of the selected pixel regions.

The electrochromic display devices may develop various colors based onvarious structures of electrochromic compounds, and hence, they areexpected to be utilized as multicolor display device devices. An exampleof the multicolor display device utilizing the electrochromic displaydevice is disclosed in Japanese Patent Application Publication No.2003-270671 (Patent Document 4). The disclosed multicolor display deviceincludes two or more layers of electrochromic elements each having astructural unit formed by arranging an electrochromic layer and anelectrolyte layer between a pair of transparent electrodes.

In addition, Japanese Patent Application Publication No. 2010-33016(Patent Document 5) discloses another example of the multicolor displaydevice utilizing the electrochromic display. The disclosed multicolordisplay device is formed by two or more electrochromic layers between apair of a display substrate and a counter electrode. In the disclosedmulticolor display device, two or more display electrodes are providedmutually separate from each other between the pair of the displaysubstrate and the counter electrode so that the electrochromic layer isformed corresponding to each of the display electrodes.

However, the multicolor display devices utilizing the electrochromicdisplay devices disclosed in the related art seem to have room forimprovement in the following aspects.

For example, in the multicolor electrochromic display device disclosedin Patent Document 4, since the multicolor electrochromic display deviceis formed of the layers of two or more electrochromic elements, theremay be an increase in manufacturing cost compared to that of themonochrome electrochromic display device formed of one layer of theelectrochromic element. Further, since the monochrome electrochromicdisplay device formed of one layer of the electrochromic element needsto have two layers of transparent electrodes, the multicolorelectrochromic display formed of two or more layers of theelectrochromic elements may need to have twice as many as the number oflayers of the electrochromic elements, which may lower the reflectanceand the contrast.

Meanwhile, in the multicolor electrochromic display device disclosed inPatent Document 5, the electrochromic layers of the display electrodesare selectively driven to develop or dissipate a corresponding color ofthe electrochromic layer of the selected display electrode. Accordingly,the electric resistance between the display electrodes arrangedseparately from each other may need to be higher than the electricresistance within each of the display electrode surfaces. That is, ifthe electric resistance between the display electrodes is small, currentmay flow into unselected display electrodes. That is, it may not bepossible to drive the selected display electrodes to independentlydevelop or dissipate colors of the electrochromic layers of the selecteddisplay electrodes.

However, in the electrochromic display device disclosed in PatentDocument 5, it may be difficult to sufficiently obtain insulatingproperties between the display electrodes in driving the selectedelectrochromic layers corresponding to the counter electrodes toindependently develop or dissipate the corresponding colors of theselected electrochromic layers (active matrix). That is, the precedingdeveloped color of the selected electrochromic layer may have an adverseeffect on the succeeding developing color operation for developing theselected color of the electrochromic layer to be developed.

SUMMARY OF THE INVENTION

It is a general object of at least one embodiment of the presentinvention to provide an information processing apparatus and aninformation processing method that substantially eliminate one or moreproblems caused by the limitations and disadvantages of the related art.

It is a general object of at least one embodiment of the presentinvention to provide an electrochromic display device having a structuresimpler than the electrochromic display device having two or more layersof the electrochromic elements, and capable of independently developingor dissipating desired colors. In one embodiment, there is provided anelectrochromic display device that includes a display substrate; acounter substrate facing the display substrate; an array of counterelectrodes formed on the counter substrate; at least a first displayelectrode and a second display electrode arranged between the displaysubstrate and the array of the counter electrodes, the first displayelectrode and the second display electrode having a predetermineddistance from each other; a first electrochromic layer arranged on thefirst display electrode and a second electrochromic layer arranged onthe second display electrode; an electrolyte layer arranged between thefirst and the second display electrodes and the array of the counterelectrodes; and a protective layer made of an insulator material formedon a counter electrode facing a side surface of one of the first and thesecond display electrodes such that the protective layer is sandwichedbetween the selected one of the first and the second display electrodesand a corresponding one of the first and the second electrochromiclayers.

In another embodiment, there is provided a method for manufacturing theelectrochromic display device. The manufacturing method includes formingthe protective layer by vacuum deposition.

In another embodiment, there is provided a method for driving theelectrochromic display device. The driving method includes applyingvoltages between the first and the second display electrodes and thecorresponding counter electrodes in the order of distance from farthestto closest between the first and the second display electrodes and thecorresponding counter electrodes to subsequently drive the first and thesecond electrochromic layers to develop corresponding colors.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of embodiments will be apparent fromthe following detailed description when read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross-sectional diagram schematically illustrating aconfiguration of an electrochromic display device according to anembodiment;

FIG. 2 is a cross-sectional diagram schematically illustrating a statein which the electrochromic display device according to the embodimentis driven to develop color;

FIG. 3 is a cross-sectional diagram schematically illustrating a statein which a comparative example of the electrochromic display device isdriven to develop color;

FIG. 4 is a flowchart illustrating steps of a method for manufacturingthe electrochromic display device according to the embodiment;

FIG. 5 is a flowchart illustrating steps of a method for driving theelectrochromic display device according to the embodiment; and

FIG. 6 is a diagram schematically illustrating a configuration of anelectrochromic display device utilized in Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the accompanying drawings.

(Electrochromic Display Device)

Next, the electrochromic display device according to an embodiment isdescribed with reference to FIG. 1. FIG. 1 is a cross-sectional diagramschematically illustrating a configuration of the electrochromic displaydevice according to the embodiment.

As illustrated in FIG. 1, an electrochromic display device 10 includes adisplay substrate 11, display electrodes 11 a, 11 b and 11 c, a countersubstrate 12, counter electrodes 12 a, electrochromic layers 13 a, 13 band 13 c, insulator layers 14 a and 14 b, protective layers 15 a, 15 band 15 c, an electrolyte layer 16, and a white reflective layer 17.

The display substrate 11 is utilized for supporting the above layeredstructure of the electrochromic display device 10.

The display electrodes 11 a, 11 b and 11 c are provided from the displaysubstrate 11 side to the counter electrode 12 a side such that thedisplay electrodes 11 a, 11 b and 11 c and the counter electrodes 12 aare mutually arranged at predetermined intervals. The display electrode11 a is formed on the counter electrodes 12 a facing side of the displaysubstrate 11. The display electrodes 11 a, 11 b and 11 c are configuredto control an electric potential to be applied to the counter electrodes12 a such that colors of the electrochromic layers 13 a, 13 b and 13 care formed (developed).

The counter substrate 12 is provided such that the counter substrate 12faces the display substrate 11 via a predetermined interval. The counterelectrodes 12 a are formed on the display substrate 11 facing side ofthe counter substrate 12.

The electrochromic layers 13 a, 13 b and 13 c are respectively formed onthe counter electrodes 12 a facing side of the display electrodes 11 a,11 b and 11 c. The electrochromic layers 13 a, 13 b and 13 c develop ordissipate colors by redox reaction (oxidation-reduction reaction).

The insulator layers 14 a and 14 b are formed on the counter electrodes12 a facing side of the electrochromic layers 13 a and 13 b. Theinsulator layers 14 a and 14 b are configured to retain the insulatingproperties between the display electrodes 11 a, 11 b and 11 c.

The protective layers 15 a, 15 b and 15 c are respectively formed on thecounter electrodes 12 a facing side of the display electrodes 11 a, 11 band 11 c. More specifically, the protective layers 15 a, 15 b and 15 care respectively formed between the display electrodes 11 a, 11 b and 11c and electrochromic layers 13 a, 13 b and 13 c.

The electrolyte layer 16 is provided such that the electrolyte layer 16is sandwiched between the display electrode 11 a and the counterelectrodes 12 a. The electrolyte layer 16 indicates ion mobility andgenerally includes electrolyte and solvents. Further, the electrolytelayer 16 may include white pigment particles 18 so that the electrolytelayer 16 is provided with a white reflex function. In this case, thewhite reflective layer 17 may be excluded.

The white reflective layer 17 is provided for scattering light incidentfrom the display substrate 11 side.

The electrochromic display device 10 is configured to apply voltagesbetween the selected display electrodes 11 a to 11 c and the counterelectrodes 12 a such that the electrochromic layers 13 a, 13 b and 13 crespectively provided on the display electrodes 11 a to 11 c develop ordissipate colors by redox reaction on receiving electric charges fromthe display electrodes 11 a to 11 c. Further, in the electrochromicdisplay device 10, the electrochromic layers 13 a, 13 b and 13 c includewhite reflex functions at the counter electrodes 12 a facing side of theelectrochromic layers 13 a, 13 b and 13 c. Accordingly, theelectrochromic display device 10 is a reflective electrochromic devicehaving viewability from the display substrate 11 side.

Further, the electrochromic layers 13 a, 13 b and 13 c may be formed ofrespective electrochromic compounds capable of developing differentcolors such as yellow (Y), magenta (M), and cyan (C). Accordingly, theelectrochromic display device 10 may display unicolor such as Y, M, andC, or mixed color such as red (R), green (G), blue (B), and black (K).

Next, detailed configurations and materials used for units of theelectrochromic display device 10 according to the embodiment aredescribed.

The display substrate 11 may be made of glass or plastic. Specifically,when a plastic film is used as the display substrate 11, the lightweightand flexible electrochromic display device 10 may be produced.

Materials for the display electrodes 11 a to 11 c may not beparticularly limited. The display electrodes 11 a to 11 c may be formedof any materials insofar as the materials include electricalconductivity. However, it is preferable that the display electrodes 11 ato 11 c be formed of a transparent conductive material having excellenttransparency and electric conductivity. With such configurations, thedisplay electrodes 11 a to 11 c may provide excellent color viewability.Examples of the transparent conductive material include inorganicmaterials such as indium tin oxide (ITO), fluorine doped tin oxide(PTO), antimony tin oxide (ATO), and the like. Among these, preferablematerials may be inorganic materials including at least anyone of anindium oxide (hereinafter also called “In oxide”), a tin oxide(hereinafter also called “Sn oxide”) and a zinc oxide (hereinaftercalled “Zn oxide”) formed by vacuum deposition. In oxide, Sn oxide andZn oxide may be easily deposited by sputtering and may exhibit excellenttransparency and electric conductivity. Further, particularly preferablematerials for the display electrodes 11 a to 11 c may be InSnO, GaZnO,SnO, In₂O₃, and ZnO.

It is preferable that the inter-electrode resistance between any two ofthe display electrodes 11 a to 11 c be sufficiently high such that theelectric potential of one of the display electrodes 11 a to 11 ccorresponding to the counter electrodes 12 a is controlled independentlyof the electric potential of the other display electrode correspondingto the counter electrodes 12 a. Accordingly, it is preferable that thedisplay electrodes 11 a to 11 c be formed such that the inter-electroderesistance between any two of the display electrodes 11 a to 11 c ishigher than the sheet resistance of any of the display electrodes 11 ato 11 c. In a case where a voltage is applied to any of the displayelectrodes 11 a to 11 c under the condition that the electric potentialbetween any two of the display electrodes 11 a to 11 c is lower than thesheet resistance of any of the display electrodes 11 a to 11 c, theapproximately same voltage may be applied to the other displayelectrodes. As a result, the electrochromic layers 13 a to 13 ccorresponding to display electrodes may not be independently driven todevelop or dissipate colors of the electrochromic layers 13 a to 13 cindependently. It is preferable that the inter-electrode resistancebetween the display electrodes 11 a to 11 c be more than 500 timeshigher than the sheet resistance of each of the display electrodes 11 ato 11 c.

Materials for the counter substrate 12 may not be particularly limited;however, the materials used for the display substrate 11 may be used.

Materials for the counter electrodes 12 a may not be particularlylimited. The counter electrodes 12 a may be formed of any materialsinsofar as the materials include electrical conductivity. In a casewhere the counter substrate 12 is made of glass or a plastic film, thecounter electrodes 12 a may be formed of a transparent conductive filmsuch as ITO, FTO or a zinc oxide, a metallic conductive film such aszinc or platinum, or carbon. the counter electrodes 12 a made of thetransparent conductive film or metallic conductive film may de formed byvacuum deposition or wet coating. On the other hand, in a case where thecounter substrate 12 is made of the metallic sheet such as zinc, thecounter substrate 12 may also serve as the counter electrodes 12 a.

As materials for the counter electrodes 12 a, the materials that inducereaction reverse of the redox reaction generated in the electrochromiclayers 13 a to 13 c may be utilized. In this case, the electrochromiclayers 13 a to 13 c may be stably driven to develop or dissipate theircolors. That is, the materials that induce reduction reaction when theelectrochromic layers 13 a to 13 c develop colors by oxidation reaction,and induce oxidation reaction when the electrochromic layers 13 a to 13c develop colors by reduction reaction may be utilized as the counterelectrodes 12 a or may be utilized by being formed on the surfaces ofthe counter electrodes 12 a. With such configurations, theelectrochromic layers 13 a to 13 c may be reliably induce reactions todevelop or dissipate their colors.

The electrochromic layers 13 a, 13 b and 13 c may be formed of materialsthat change colors by redox reaction (oxidation-reduction reaction).Examples of such materials include electrochromic compounds such aspolymer series, pigment series, metal complex compounds, and metallicoxides known to the art.

Specific examples of the polymer and pigment electrochromic seriesinclude low molecular organic electrochromic compounds such asazobenzene series, anthraquinone series, diarylethene series,dihydroprene series, styryl series, styryl spiropyran series,spirooxazine series, spiro thiopyran series, thioindigo series,tetrathiafulvalene series, terephthalic acid series, triphenylmethaneseries, triphenyl amine series, naphthopyran series, viologen series,pyrazoline series, phenazine series, phenylene diamine series,phenoxazine series, phenothiazine derivative phthalocyanine series,fluorane series, fulgide series, benzopyran series, the metalloceneseries compounds, or high molecular compounds such as polyaniline andpolythiophene compounds.

Among these, the dipyridine series compounds represented by thefollowing general formula (1) are particularly preferable.

wherein R₁ and R₂ independently represent an alkyl group having 1 to 8carbon atoms, which may have a substituent; or an aryl group having 1 to8 carbon atoms, which may have a substituent, and at least one of R₁ andR₂ includes a substituent selected from COOH, PO(OH)₂, andSi(OC_(k)H_(2k+1))₃; X represents a monovalent anion; n, m and 1independently represent 0 or 1; k represents one of 0, 1 and 2; A, B andC independently represent an aryl group or a heterocyclic group having 2to 20 carbon atoms, which may have a substituent. The above materialsinclude low electric potential to develop or dissipate colors.Accordingly, these materials may exhibit a feasible color value when theelectrochromic display device 10 includes plural display electrodes.

The electrochromic compounds in the electrochromic layers 13 a to 13 cmay be adsorbed to or bonded to a semiconductor material having ananostructure with a nano-meter order particle size (hereinafter calleda “nanostructure semiconductor material”). Further, the electrochromiccompounds and the nanostructure semiconductor material may be mixed toform a single layer.

Materials for the nanostructure semiconductor material may include butnot be particularly limited to metallic oxides including a zinc oxide, atin oxide, an aluminum oxide (hereinafter called “alumina”), a zirconiumoxide, a cerium oxide, a silicon oxide (hereinafter called “silica”),oxidation yttrium, oxygen boron, a magnesium oxide, strontium titanate,potassium titanate, barium titanate, calcium titanate, a calcium oxide,ferrite, oxidation hafnium, a tungsten oxide, an iron oxide, copperoxide, nickel oxide, cobalt oxide, barium oxide, strontium oxide,oxidation vanadium, alumino silicic acids, or calcium phosphates as amajor component. The above metallic oxides may be used alone or incombination of two or more. In view of physical properties such as anoptical property or electric characteristics such as electricconductivity, in a case where one of or a combination of two or moreselected from a titanium oxide, a zinc oxide, a tin oxide, alumina, azirconium oxide, an iron oxide, a magnesium oxide, oxidation indium, anda tungsten oxide is used as the nanostructure semiconductor material,the electrochromic layers may exhibit multicolor with excellent colordeveloping or dissipating responsiveness.

Further, the shape of the nanostructure semiconductor material may notbe particularly specified but may preferably include a large surfacearea per unit volume (hereinafter called a “specific surface area”) forefficiently carrying the electrochromic compounds. If the electrochromiclayers 13 a to 13 c have large specific surface areas, theelectrochromic layers 13 a to 13 c may efficiently carry theelectrochromic compounds, thereby exhibiting an excellent contrast ratioin developing or dissipating colors.

A film thickness of the electrochromic layers 13 a, 13 b and 13 c may bepreferably in a range of 0.2 to 50 μm. The electrochromic layers 13 a,13 b and 13 c having the film thickness less than 0.2 μm may not exhibithigh color development density. Further, the electrochromic layers 13 a,13 b and 13 c having the film thickness more than 50 μm may lower colorviewability of the electrochromic device 10 due to coloring of theelectrochromic layers 13 a to 13 c as well as increasing manufacturingcost of the electrochromic display device 10.

Materials for the insulator layers 14 a and 14 b may not be particularlyspecified but may be formed of any materials insofar as they are aporous film; however, organic or inorganic materials having excellentinsulation, durability, and film formability may be used.

The insulator layers 14 a and 14 b formed of porous films may be formedby any film forming methods known in the art including various methodsdescribed below. For example, the insulator layers 14 a and 14 b may beformed by sintering in which polymeric microparticles or inorganicparticles are partially fusion-bonded by mixing a binder or the like toform pores between the particles. Further, the insulator layers 14 a and14 b may be formed by extraction in which a structural layer isinitially formed of organic or inorganic materials soluble in solventsand a binder insoluble in solvents, and the organic or inorganicmaterials of the structural layer are then dissolved in the solvents toform pores. Moreover, the insulator layers 14 a and 14 b may be formedby a foaming method in which a high molecular weight polymer is put in afoam state by heating or degassing. Further, the insulator layers 14 aand 14 b may be formed by phase transition in which a polymer mixturemay be phase-separated by controlling a good solvent and a poor solvent.In addition, the insulator layers 14 a and 14 b may be formed byirradiation in which the polymer is irradiated to form pores.

Examples of the porous film include a polymer mixture particle filmformed of inorganic nanostructure particles (SiO₂ particles, Al₂O₃particles) and polymer binder, an organic porous film (polyurethaneresin, polyethylene resin), or the like.

In addition, an inorganic insulator film may be formed on the porousfilm. The inorganic insulator film may be formed of materials at leastincluding ZnS. With the materials containing ZnS, the inorganicinsulator film may be formed at higher rates by sputtering withoutdamaging the electrochromic layers 13 a to 13 c. Further, examples ofthe materials containing ZnS as a major component include ZnO—SiO₂,ZnS—SiC, ZnS—Si, and ZnS—Ge. Note that it is preferable that the contentof ZnS in the above materials be approximately in a range of 50 to 90mol % to reasonably maintain crystallinity of the insulator layers 14 aand 14 b. Accordingly, particularly preferable examples of the materialscontaining ZnS include ZnS—SiO₂ (8/2), ZnS—SiO₂ (7/3), ZnS, andZnS—ZnO—In₂O₃—Ga₂O₃ (60/23/10/7).

Since the above materials are used for the insulator layers 14 a and 14b, the film thickness of the insulator layers 14 a and 14 b necessaryfor maintaining feasible insulation may be decreased. Accordingly, evenwhen the insulator layers 14 a and 14 b are layered to form a thickfilm, the insulator layers 14 a and 14 b may not come off due to theincreased thickness of the film.

As already described above, when the ZnS film is formed by sputtering, aporous particle film may be formed in advance as an under coat layer(UCL) to form a porous ZnS film. In this case, the aforementionednanostructure semiconductor material may be used as the porous particlefilm. Note that it is preferable that the insulator layers 14 a and 14 bhave a two-layer structure including the porous particle film and aseparately formed porous film containing silica and alumina in order toreasonably maintain the insulation of the insulator layers 14 a and 14b. Since the insulator layers 14 a and 14 b are formed of the porousfilms, the electrolyte layer 16 may penetrate the insulator layers 14 aand 14 b, and the display electrodes 11 a to 11 c, which may facilitatemigration of ionic charges in the electrolyte layer 16 with the redoxreaction. As a result, the electrochromic display device 10 may beimplemented as a multicolor display device with excellent colordeveloping or dissipating responsiveness.

The film thickness of the insulator layers 14 a and 14 b may bepreferably in a range of 20 to 2000 nm. If the film thickness of theinsulator layers 14 a and 14 b is less than 20 nm, the insulation of theinsulator layers 14 a and 14 b may not be maintained. If the filmthickness of the insulator layers 14 a and 14 b exceeds 2000 nm, colorviewability of the electrochromic device 10 may decrease due to coloringof the electrochromic layers 13 a to 13 c as well as increasingmanufacturing cost of the electrochromic display device 10.

Note that in a case where the inter-electrode resistance between thedisplay electrodes 11 a to 11 c is increased by increasing the filmthicknesses of the electrochromic layers 13 a to 13 c, the insulatorlayers 14 a and 14 b may be excluded.

The protective layers 15 a, 15 b and 15 c are formed of the insulatormaterial and respectively formed between the display electrodes 11 a, 11b and 11 c and the electrochromic layers 13 a, 13 b and 13 c. That is,the protective layers 15 a to 15 c are formed on the respective counterelectrodes 12 a facing side surfaces of the display electrodes 11 a to11 c such that the protective layers 15 a to 15 c are sandwiched betweenthe display electrodes 11 a to 11 c and the electrochromic layers 13 ato 13 c, respectively.

In a case where the electrochromic layers 13 a to 13 c are formed byallowing the electrochromic compounds to be adsorbed to or bond to thenanostructure semiconductor material, the protective layers 15 a to 15 cmay be formed on the surfaces of the display electrodes 11 a to 11 c orthe nanostructure semiconductor materials. Note that it is preferablethat the protective layers 15 a to 15 c be formed on the surfaces of thedisplay electrodes 11 a to 11 c.

The protective layers 15 a to 15 c may be formed of organic or inorganicinsulator materials. However, it is preferable that the displayelectrodes 11 a to 11 c be formed of the inorganic materials having ametallic oxide as a major component in view of exhibiting excellentinsulation as the insulator materials. Note that the materials havinginsulation may include a wide band gap and be less likely to carry anelectric current when a direct voltage is applied to those materials.Examples of the organic materials include polymeric materials such aspolyethylene, polyvinyl chloride, polyester, epoxy resin, melamineresin, phenolic resin, polyurethane resin, and polyimide resin. Examplesof the inorganic materials include materials known to the art such asSiO₂, HfO₂, Ta₂O₅, Al₂O₃, ZrO₂, Si₃N₄, and ZnS, or combinations of thesematerials. Among these, the materials containing an Al oxide or a Sioxide may be particularly preferable. The materials containing an Aloxide or a Si oxide exhibit excellent insulation, so that it may be easyto independently drive a selected one of the electrochromic layers 13 ato 13 c to develop or dissipate its corresponding color even if theelectrochromic layer is thin.

The film thickness of the protective layers 15 a to 15 c may preferablybe in a range of 0.5 to 500 nm, and also preferably be less than thefilm thickness of the display electrodes 11 a to 11 c on which theprotective layers 15 a to 15 c are respectively formed. If the filmthickness of the protective layers 15 a to 15 c is less than 0.5 nm, theinsulation of the protective layers 15 a to 15 c may not be maintained.If the film thickness of the protective layers 15 a to 15 c exceeds 500nm, the electrochromic layers 11 a to 11 c may not develop or dissipatecolors due to a decrease in the penetration of electrolytes from theelectrolyte layer 16 into the electrochromic layers 13 a to 13 c as wellas a decrease in the migration of the electric charges from the displayelectrodes 11 a to 11 c to the electrochromic layers 13 a to 13 c.Further, if the protective layers 15 a to 15 c include the filmthicknesses greater than those of the display electrodes 11 a to 11 c,the pores of the porous display electrodes 11 a to 11 c may be clogged,thereby lowering the penetration of the electrolytes into theelectrochromic layers 13 a to 13 c. If the protective layers 15 a to 15c are formed of inorganic materials having a metallic oxide as a majorcomponent, the film thickness of the protective layers 15 a to 15 c maypreferably be in a range of 0.5 to 20 nm, and particularly preferably bein a range of 0.5 to 5 nm. If the film thickness of the protectivelayers 15 a to 15 c exceeds 5 nm, color development or dissipationdriving rates may easily be decreased. Further, it is preferable thatthe protective layers 15 a, 15 b and 15 c be formed such that the filmthicknesses of the protective layers 15 a, 15 b and 15 c vary with therespective display electrodes 11 a to 11 c based on color development ordissipation properties of the electrochromic layers 13 a to 13 c and theelectrical conductivity of the electrochromic layers 13 a to 13 c. Notethat the protective layers may not be formed on all the displayelectrodes 11 a to 11 c.

Note also that if the color development or dissipation properties of theelectrochromic layers 13 a to 13 c are decreased due to contact with(adsorption and bonding to) the protective layers 15 a to 15 c, it ispreferable that surface layers further be formed on the surfaces of theprotective layers 15 a to 15 c. The surface layers may be formed of atransparent conductive material such as ITO that is similar to materialsof the display electrodes.

The electrolyte layer 16 may be formed by dissolving supportingelectrolytes into solvents so as to increase ionic conductance. Examplesof the supporting electrolytes include alkali metal salts, inorganic ionsalts such as alkaline earth metal salts, quarternary ammonium salts oracids, and alkaline supporting electrolytes. Specific examples of thesupporting electrolytes include LiClO₄, LiBF₄, LiAsF₆, LiPF₆, LiCF₃SO₃,LiCF₃COO, KCl, NaClO₃, NaCl, NaBF₄, NaSCN, KBF₄, Mg(ClO₄)₂, Mg(BF₄)₂,and tetrabutylammonium perchlorate. Further, examples of the solventsinclude propylene carbonate, acetonitrile, γ-butyrolactone, ethylenecarbonate, sulfolane, dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,2-dimethoxyethane,1,2-ethoxymethoxy ethane, polyethylene glycol, and alcohols. Note thatthe electrolyte layer 16 may not be limited to the liquid electrolytesformed by dissolving the supporting electrolytes into the solvents. Theelectrolyte layer 16 may be formed of ionic liquid, gelatinouselectrolytes, solid electrolytes such as polymer electrolytes, and thelike.

On the other hand, it may be preferable to use gelatinous or solidelectrolyte layer 16 in order to improve element strength andreliability, and to prevent color development diffusion. The electrolytelayer 16 may be formed solid by retaining the electrolytes and solventsin the polymeric resin. The electrolyte layer 16 formed by retaining theelectrolytes and solvents in the polymeric resin may exhibit high ionicconductance and strength. A preferable example of the polymeric resinincludes photo-curable (photo-setting) resin. The electrolyte layer 16made of the photo-curable resin may be formed at lower temperatures andin a short time compared to that made of thermosetting resin, which maybe formed by evaporating the solvents of the materials of theelectrolyte layer 16 or by allowing the materials of the electrolytelayer 16 to undergo thermal polymerization in order to reduce the filmthickness of the electrolyte layer 16. Examples of the photo-curableresin include, but are not limited to, urethane, ethylene glycol,polypropylene glycol, vinyl alcohol, acrylic, and epoxy.

The electrolyte layer 16 may be provided with a function of the whitereflective layer 17 by dispersing white pigment particles 18 into theelectrolyte layer 16. Examples of the white pigment particles 18include, but not limited to, metallic oxides such as a titanium oxide,an aluminum oxide, a zinc oxide, a silicon oxide, oxidation cesium, andoxidation yttrium. If the amount of the white pigment particles 18contained in the electrolyte layer 16 is large, light applied to theelectrolyte layer 16 to cure the photo-curable resin may be blocked bythe white pigment particles 18 contained in the electrolyte layer 16.Accordingly, the photo-curable resin may not be efficiently cured. Theamount of the white pigment particles 18 contained in the electrolytelayer 16 may vary with the thickness of electrolyte layer 16; however,it is preferable that the amount of the white pigment particles 18contained in the electrolyte layer 16 be in a range of 10 to 50 wt %.

Further, a film thickness of the electrolyte layer 16 may be preferablyin a range of 0.1 to 200 μm, and particularly preferably in a range of 1to 50 μm. If the film thickness of the electrolyte layer 16 is less than1 μm, it becomes difficult to maintain the electrolytes in the layer 16.On the other hand, if the film thickness of the electrolyte layer 16exceeds 50 μm, electric charges may become easy to diffuse into the partin the outside regions of the pixels selected by the electrolyte layer16.

Materials of the white reflective layer 17 may include an inorganiccompound film formed of oxides, nitrides, and sulfides by vacuumdeposition, or a film formed of metal oxide particles such as a titaniumoxide, an aluminum oxide, a zinc oxide, a silicon oxide, oxidationcesium, oxidation yttrium as well as metal and a metalloid. Further, itis preferable that the white reflective layer 17 formed of the inorganiccompound film have a structure similar to those of the insulator layers14 a and 14 b in order for the white reflective layer 17 to acquireelectrolyte permeability. In addition, the metal oxide particle film maybe easily formed by depositing the paste obtained by dispersing metallicoxide particles in a solution. Titanium oxide particles may beparticularly preferable as the metallic oxide particles.

Note that a film thickness of the white reflective layer 17 may bepreferably in a range of 0.1 to 50 μm, and particularly preferably in arange of 0.5 to 5 μm. The white reflective layer 17 having the filmthickness less than 0.5 μm may not sufficiently exhibit the whitereflecting effect. Further, the white reflective layer 17 having thefilm thickness more than 5 μm may not retain electrolyte permeabilityand film strength simultaneously.

Moreover, if the film thickness of the white reflective layer 17 formedof titanium oxide particles is increased until the white reflectivityreaches the maximum, the film strength may be lowered. Thus, it ispreferable that the white reflective layer 17 be formed of a two-layerstructure that includes the white reflective layer 17 for securing thefilm strength and a white electrolyte layer obtained by mixing the whitepigment particles 18 with the electrolyte layer 16.

Next, a method for independently developing color of one of theelectrochromic layers 13 a to 13 c subsequently driven while maintainingthe developed color of another one of the electrochromic layers 13 a to13 c initially driven is described with reference to FIGS. 2 and 3. FIG.2 is a cross-sectional diagram schematically illustrating a state inwhich the electrochromic display device 10 according to the embodimentis driven to develop color. FIG. 3 is a cross-sectional diagramschematically illustrating a state in which a comparative example of anelectrochromic display device 110 is driven to develop color. Note thatwhite space regions A and B indicate color development regions in FIGS.2 and 3.

As illustrated in FIGS. 2 and 3, the counter electrodes 12 a includecounter pixel electrodes 12 a-1 and 12 a-2 in each of the electrochromicdisplay devices 10 and 110. Further, the respective counter pixelelectrodes 12 a-1 and 12 a-2 are associated with the white space regions(indicated as A and B), respectively, in each of the electrochromicdisplay devices 10 and 110.

As a driving method for developing color, the following examples may beconsidered. As illustrated in FIG. 2, in the electrochromic displaydevice 10, a voltage is applied between the counter pixel electrode 12a-1 and the first display electrode 11 a to initially drive the A regionof the first electrochromic layer 13 a to develop color. Thereafter, avoltage is applied between the counter pixel electrode 12 a-2 and thesecond display electrode 11 b to subsequently drive the B region of thesecond electrochromic layer 13 b to develop color.

Before further illustrating the electrochromic display device 10according to the embodiment, the comparative example of theelectrochromic display device 110 that includes no protective layers isexamined by referring to FIG. 3. In the comparative example of theelectrochromic display device 110, when a voltage is applied between thecounter pixel electrode 12 a-2 and the second display electrode 11 b,the A region of the second electrochromic layer 13 b develops colorwhile there is failure to maintain the developed color in a notillustrated A region of the first electrochromic layer 13 a asillustrated in FIG. 3.

In the above case, when the A region of the first electrochromic layer13 a is driven to develop color, electrolytic ions migrate. Accordingly,the insulation between the first and second display electrodes 11 a and11 b is not maintained due to the voltage applied for developing the Bregion of the second electrochromic layer 13 b.

In contrast, in the electrochromic display device 10 according to theembodiment, the protective layer 15 a formed of the insulator materialis provided between the first display electrode 11 a and the firstelectrochromic layer 13 a as illustrated in FIG. 2. With thisconfiguration, the protective layer 15 a may prevent the colordevelopment charges of the first electrochromic layer 13 a from movingback to the first display electrode 11 a. Thus, the developed color ofthe region A of the first electrochromic layer 13 a may be maintainedeven when the insulation (voltage resistance) is unstable. Further, withthis configuration, the insulation (voltage resistance) between thefirst and second display electrodes 11 a and 11 b is improved.Accordingly, when a voltage is applied between the counter pixelelectrode 12 a-2 and the second display electrode 11 b, a notillustrated A region of the second electrochromic layer 13 b may beprevented from developing color as illustrated in FIG. 2. As a result,the B region of the second electrochromic layer 13 b may independentlydevelop color while maintaining the developed color of the A region ofthe first electrochromic layer 13 a as illustrated in FIG. 2.

As described above, the electrochromic display device according to theembodiment includes a structure simpler than the electrochromic displaydevice having two or more layers of the electrochromic elements. In theelectrochromic display device 10 having such a configuration, desiredcolor may be developed in one of the electrochromic layers 13 a to 13 crespectively formed on the display electrodes 11 a to 11 c by applying avoltage between a selected one of the display electrodes 11 a to 11 cand the counter electrodes 12 a.

Further, in the electrochromic display device 10 having such aconfiguration, the counter pixel electrodes 12 a are formed as activematrix driven pixel electrodes. Accordingly, the electrochromic displaydevice 10 may be formed as an active-matrix display device.

(Manufacturing Method for Electrochromic Display Device)

Next, a method for manufacturing the electrochromic display deviceaccording to the embodiment is described with reference to FIG. 4. FIG.4 is a flowchart illustrating steps of the method for manufacturing theelectrochromic display device according to the embodiment.

As illustrated in FIG. 4, the method for manufacturing theelectrochromic display device according to the embodiment includesforming a display electrode (step S11), forming a protection layer (stepS12), forming an electrochromic layer (step S13), forming an insulatorlayer (step S14), forming a white state reflectance layer (step S15),forming counter electrodes (step S16), forming an electrolyte layer(step S17), and bonding a display substrate and a counter substrate(step S18).

More specifically, in step S11, a display electrode 11 a is formed on adisplay substrate 11 by vacuum deposition such as vapor-deposition,sputtering, and ion-plating.

In step S12, a protective layer 15 a is formed on the display substrate11 on which the display electrode 11 a is formed. The protective layer15 a may be easily formed by any process known in the art such as vacuumdeposition, coating, inkjet coating, and printing. Among these, it maybe particularly preferable to prepare the display electrode 11 a formedof the metallic oxide film by vacuum deposition. With the vacuumdeposition, it may be possible to increase the productivity inmanufacturing the electrochromic display unit 10 by sequentiallydepositing the display electrode 11 a and the protective layer 15 a.

In step S13, an electrochromic layer 13 a is formed by printing such asspin-coating or screen-printing on the display substrate 11 on which thedisplay electrode 11 a and the protective layer 15 a are formed.

In step S14, an insulator layer 14 a is formed by vacuum deposition suchas vapor-deposition, sputtering and ion-plating or by printing such asspin-coating and screen-printing on the display substrate 11 on whichthe display electrode 11 a, the protective layer 15 a and theelectrochromic layer 13 a are formed.

As described above, in steps S11 to S14, a first layer including thedisplay electrode (or first display electrode) 11 a, the protectivelayer (or first protective layer) 15 a, the electrochromic layer (orfirst electrochromic layer) 13 a, and the insulator layer (firstinsulator layer) 14 a may be formed on the display substrate 11. Notethat in the method for manufacturing the electrochromic display deviceaccording to the embodiment, steps S11 to S14 are repeated twice. As aresult, the display electrodes 11 a to 11 c, the protective layers 15 ato 15 c, the electrochromic layers 13 a to 13 c and the insulator layers14 a and 14 b are formed on the display substrate 11 in a direction fromthe display substrate 11 side to the counter electrode 12 a side suchthat the display electrodes 11 a to 11 c and the counter electrodes 12 aare mutually arranged at predetermined intervals as illustrated in FIG.1.

Note that an insulator layer may not be formed in a third layer formedof the display electrode 11 c, the protective layer 15 c and theelectrochromic layer 13 c. That is, the insulator layer forming step(step S14) may be omitted from forming of the third layer. Theelectrochromic display device 10 illustrated in FIG. 1 includes noinsulator layer in the third layer that is formed of the displayelectrode 11 c, the protective layer 15 c and the electrochromic layer13 c. Note that the first layer includes the first display electrode 11a, the first protective layer 15 a, the first electrochromic layer 13 aand the first insulator layer 14 a; a second layer includes a seconddisplay electrode 11 b, a second protective layer 15 b, a secondelectrochromic layer 13 b and a second insulator layer 14 b; and thethird layer includes a third display electrode 11 c, a third protectivelayer 15 c, and a third electrochromic layer 13.

In step S15, a white reflective layer 17 is formed by printing such asspin-coating or screen-printing on the display substrate 11 on which thedisplay electrode 11 a through an electrochromic layer 13 c are formed.

In step S16, counter electrodes 12 a are formed on a counter substrate12 by vacuum deposition such as vapor-deposition, sputtering, andion-plating. Note that if the counter electrodes 12 a are formed oforganic materials, the counter electrodes 12 a may be formed by printingsuch as spin-coating or screen-printing.

In step S17, an electrolyte layer 16 is formed on the counter substrate12 on which the counter electrodes 12 a are formed. The electrolytelayer 16 is formed by coating dispersion paste containing an electrolyteon the counter substrate 12 on which the counter electrodes 12 a areformed.

In step S18, the display substrate 11 on which the display electrode 11a through white reflective layer 17 are formed and the counter substrate12 on which the counter electrodes 12 a and the electrolyte layer 16 areformed are bonded. More specifically, in step S18, the display substrate11 and the counter substrate 12 may be bonded by applying UV light fromthe counter substrate 12 side so that a UV curable adhesive contained inthe electrolyte layer 16 is cured.

(Driving Method for Electrochromic Display Device)

Next, a method for driving the electrochromic display device accordingto the embodiment is described with reference to FIG. 5. FIG. 5 is aflowchart illustrating steps of the method for driving theelectrochromic display device according to the embodiment.

As illustrated in FIG. 5, the method for driving the electrochromicdisplay device according to the embodiment includes driving a firstelectrochromic layer (step S21), driving a second electrochromic layer(step S22), and driving a third electrochromic layer (step S23).

More specifically, in step S21, a voltage is applied between the firstdisplay electrode 11 a in the first layer and a counter electrode 12 acorresponding to a desired region of the first electromic layer 13 a inthe first layer. Then, the desired region of the first electromic layer13 a in the first layer is driven to develop or dissipate color.

Subsequently, in step S22, a voltage is applied between the seconddisplay electrode 11 b in the second layer and a counter electrodes 12 acorresponding to a desired region of the second electromic layer 13 b inthe second layer. Then, the desired region of the second electromiclayer 13 b in the second layer is driven to develop or dissipate color.

Next, in step S23, a voltage is applied between the third displayelectrode 11 c in the third layer and a counter electrodes 12 acorresponding to a desired region of the third electromic layer 13 c inthe third layer. Then, the desired region of the third electromic layer13 c in the third layer is driven to develop or dissipate color.

The method for driving the electrochromic display device according tothe embodiment includes driving of the first to third electrochromiclayers 13 a to 13 c to develop color by subsequently applying voltagesbetween the first to third display electrodes 11 a to 11 c and thecorresponding counter electrodes 12 a in the order of distance fromfarthest to closest between the first to third display electrodes 11 ato 11 c and the corresponding counter electrodes 12 a. That is, thefirst to third electrochromic layers 13 a to 13 c formed on the first tothird display electrodes 11 a to 11 c are driven to developcorresponding color in the order where the display electrode (11 a, 11b, or 11 c) has a longer distance from the corresponding counterelectrodes 12 a. That is, the first to third electrochromic layers 13 ato 13 c are driven to develop the corresponding colors in the order ofthe first electrochromic layer 13 a, the second electrochromic layer 13b and the third electrochromic layer 13 c. When a voltage is appliedbetween one of the display electrodes 11 a to 11 c (the second displayelectrode 11 b in this case), the display electrode (the first displayelectrode 11 a in this case) having a distance from the counterelectrodes 12 a longer than the distance from the counter electrodes 12a that the second electrode 11 b has may be less likely to be affectedby the applied voltage. Accordingly, the selected electrochromic layer(e.b., electrochromic layer 13 b) may be independently driven (fromother electrochromic layers) to develop the corresponding color.

Note that in a case where the inter-electrode insulation between thedisplay electrodes 11 a to 11 c is secured by increasing the filmthicknesses of the protective layers 15 a to 15 c, the driving order ofthe electrochromic layers 13 a to 13 c may be changed into any order.For example, voltages may be applied simultaneously between the displayelectrodes 11 a to 11 c and the corresponding counter electrodes 12 a todrive the first electrochromic layers 13 a to 13 c to developcorresponding color simultaneously (i.e., steps S21 through S23 aresimultaneously carried out). Alternatively, the first to thirdelectrochromic layers 13 a to 13 c may be driven to developcorresponding colors in the order of distance from closest to farthestbetween the display electrodes (11 a, 11 b, or 11 c) and thecorresponding counter electrodes 12 a. That is, the first to thirdelectrochromic layers 13 a to 13 c are driven to develop thecorresponding colors in the order of the third electrochromic layer 13c, the second electrochromic layer 13 b and the first electrochromiclayer 13 a (in the order of steps S23, S22 and S21).

In dissipating color, voltages may be applied between the displayelectrodes 11 a to 11 c and the corresponding counter electrodes 12 a todrive the first to third electrochromic layers 13 a to 13 c to dissipatecorresponding colors in any order. However it is preferable that thevoltages be simultaneously applied between the display electrodes 11 ato 11 c and the corresponding counter electrodes 12 a to drive the firstto third electrochromic layers 13 a to 13 c to dissipate correspondingcolors simultaneously. In this manner, driving time for dissipatingcolor may be reduced.

EXAMPLES

Advantages and embodiments are further illustrated by the followingexamples, but the particular materials and amounts thereof recited inthese examples, as well as other conditions and details, should not beconstrued to unduly limit this invention.

Example 1 Manufacture of Electrochromic Display Device

<Formation of Display Electrode/Protective Layer/ElectrochromicLayer/Insulator Layer/White Reflective Layer>

An example 1 of the electrochromic display device 10 illustrated in FIG.1 was produced as follows. Initially, a 40×40 mm glass substrate havingthe thickness of 0.7 mm was prepared as the display substrate 11, and anITO (Indium Tin Oxide) film of approximately 100 nm in thickness wasthen formed on the glass substrate by sputtering to form the firstdisplay electrode 11 a in the first layer. Further, an Al₂O₃ (aluminiumoxide) film of approximately 5 nm in thickness was formed on a surfaceof the first display electrode 11 a in the first layer by sputtering toform the first protective film 15 a.

A dispersion liquid of titanium oxide nano-particles (Product name:SP210 produced by Showa Titanium Co., Ltd., mean particle size:approximately 20 nm) was applied onto the display electrode 11 a byspin-coating and annealing was conducted at 120° C. for 15 minutes toform a nanostructure semiconductor material formed of a titaniumoxide-particle film having approximately 1.5 μm in thickness.Subsequently, a solution 0.8 wt % 2,2,3,3-tetrafluoropropanol (TFP) of acompound 2 represented by the following formula (2) was applied onto thenanostructure semiconductor material (i.e., titanium oxide-particlefilm) by spin-coating and annealing was conducted at 120° C. for 10minutes so that electrochromic compound was adsorbed onto a surface ofthe titanium oxide-particle film to form the first electrochromic layer13 a in the first layer.

Next, 5 wt % of SiO₂ particles (Product name: NanoTek produced by KantoChemical Co., Inc, mean particle size: approximately 30 nm) weredispersed into a solvent prepared by mixing γ-butyl lactone andpropylene carbonate in a 1:1 ratio in volume, and urethane resin wasfurther added as a polymer binder into the solvent to prepare coatingliquid. The coating liquid was coated by spin coating, and annealing wasconducted at 120° C. for 5 minutes to form a SiO₂ particle layer. A filmof ZnS—SiO₂ (at a molar ratio of 8/2) having approximately 30 nm inthickness was formed on the SiO₂ particle layer by sputtering to form aninsulator layer 14 a having electrolyte permeability.

Furthermore, a second display electrode 11 b, a second protective layer15 b, a second electrochromic layer 13 b and a second insulator layer 14b in the second layer were formed by following a similar method utilizedin forming the elements of the first layer, except that the secondelectrochromic layer 13 b was formed by applying a 1.0 wt %2,2,3,3-tetrafluoropropanol solution (TFP) of a compound 3 representedby the following formula (3) onto the titanium oxide-particle film byspin-coating.

Furthermore, a third display electrode 11 c, a third protective layer 15c, a third electrochromic layer 13 c and a third insulator layer 14 c inthe third layer were formed by following a similar method utilized informing the elements of the first layer, except that the thirdelectrochromic layer 13 c was formed by applying a 0.8 wt %2,2,3,3-tetrafluoropropanol (TFP) solution of a compound 4 representedby the following formula (4) onto the titanium oxide-particle film byspin-coating.

Subsequently, a 20 wt % dimethoxysulfoxide and polyethylene glycol(Molecular weight 200) solution, urethane paste (Product name: HW140SFproduced by DIC Corporation) and tetrabutylammonium perchlorate wasmixed as polymer binder and electrolytes in a2,2,3,3-tetrafluoropropanol (TFP) solution, and 30 wt % of titaniumoxide particles (Product name: CR50 produced by Ishihara Sangyo Co.Ltd., Mean particle size: approximately 250 nm) were further dispersedinto the obtained mixture to prepare paste. The paste was coated on thethird electrochromic layer 13 c in the third layer by spin coating, andannealing was conducted at 120° C. for 5 minutes to form a whitereflective layer of approximately 1 μm in thickness.

<Formation of Counter Electrode/Electrolyte Layer>

A 32×40 mm glass substrate with a thickness of 0.7 mm was prepared asthe counter substrate 12. An ITO film having 6 line portions with afull-width of 35 mm (line width: 4 mm, space width: 1 mm) was formed bysputtering such that the ITO film has a thickness of an approximately 10nm to form the counter electrodes 12 a on the counter substrate 12.

Subsequently, a solution was prepared by mixing tetrabutylammoniumperchlorate as a electrolyte, dimethoxysulfoxide and polyethylene glycol(Molecular weight 200) as solvents and UV-curable adhesive (Productname: PTC10 produced by Jujo Chemical Co., Ltd.) at ratios of1.2:5.4:6:16, and 20 wt % of white titanium oxide particles (Productname: CR50 produced by Ishihara Sangyo Co. Ltd., Mean particle size:approximatepu 250 nm) were dispersed into the obtained mixture toprepare paste. The obtained paste was then applied dropwise to the whitereflective layer 17. Next, the display substrate 11 was stacked on thecounter substrate 12 and UV light was applied to the stacked displaysubstrate 11 and counter substrate 12 from the counter substrate 12 sideto cure the UV curable adhesive so as to bond the display substrate 11and the counter substrate 12. As a result, the electrochromic displaydevice 10 illustrated in FIG. 1 was produced. Note that 0.2 wt % of beadspacers 19 were mixed into the electrolyte layer such that the thicknessof the electrolyte layer 16 was 10 μm.

FIG. 6 is a plan diagram illustrating a planer configuration of theelectrochromic display device 10. In FIG. 6, the first display electrode11 a, the second display electrode 11 b and the third display electrode11 c are indicated by dotted line, a dashed-dotted line and a dashed-twodotted line, respectively.

The first display electrode 11 a, the second display electrode 11 b andthe third display electrode 11 c, and the counter electrodes 12 a (i.e.,counter electrodes 12 a-1 and 12 a-2) were arranged as illustrated inFIG. 6. Other layers were all formed on an entire surface of the glasssubstrate except for first, second and third driving connection portions11 a′, 11 b′ and 11 c′ corresponding to the first, the second and thethird display electrodes 11 a, 11 b and 11 c. The sheet resistance ofthe first, second and third display electrodes 11 a, 11 b and 11 c andthe counter electrodes 12 a was 150 Ω/cm, and the resistance between thefirst, second and third display electrodes 11 a, 11 b and 11 c measuredby utilizing the first, second and third driving connection portions 11a′, 11 b′ and 11 c′ was 1 MΩ or above.

[Color Development/Dissipation Test 1]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode and the positive electrode were exchangedsuch that the positive electrode was connected to the first drivingconnection portion 11 a′ corresponding to the first display electrode 11a, and the negative electrode was connected to the counter pixelelectrode 12 a-1. A voltage of −4.5 V was then applied between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for twoseconds, which had driven the first electrochromic layer 13 a (in thefirst layer) to dissipate the developed color (magenta) completely. As aresult, the color of the first electrochromic layer 13 a had returned towhite.

Further, after the application of the voltage of 4.5 V between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for onesecond, the first display electrode 11 a and the counter pixel electrode12 a-1 were allowed to stand for five minutes without applying anyvoltage. The result indicated that the developed color (magenta) of thefirst electrochromic layer 13 a had been retained, exhibiting excellentimage retaining properties.

In addition, the white reflectance in a dissipation state was measuredfrom the display substrate 11 side using a spectrophotometer LCD-5000(manufactured by Otsuka Electronics). The white reflectance obtained was50%.

[Color Development/Dissipation Test 2]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode was connected to the second drivingconnection portion 11 b′ corresponding to the second display electrode11 b (in the second layer), and the positive electrode was connected tothe counter pixel electrode 12 a-2. A voltage of 4.5 V was then appliedbetween the second display electrode 11 b and the counter pixelelectrode 12 a-2 for one second, which had driven the secondelectrochromic layer 13 b (in the second layer) to develop blue coloraccording to a shape of the counter display electrode 12 a-2 (i.e., lineportion shape). As a result, magenta and blue line portions weredisplayed.

Example 2 Manufacture of Electrochromic Display Device

An example 2 of the electrochromic display device 10 illustrated in FIG.1 was produced by following a similar method utilized in Example 1except that the protective layers 15 a to 15 c were made of SiO₂ withthickness of 10 nm.

[Color Development/Dissipation Test 1]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode and the positive electrode were exchangedsuch that the positive electrode was connected to the first drivingconnection portion 11 a′ corresponding to the first display electrode 11a, and the negative electrode was connected to the counter pixelelectrode 12 a-1. A voltage of −4.5 V was then applied between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for twoseconds, which had driven the first electrochromic layer 13 a (in thefirst layer) to dissipate the developed color (magenta) completely. As aresult, the color of the first electrochromic layer 13 a had returned towhite.

Further, after the application of the voltage of 4.5 V between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for onesecond, the first display electrode 11 a and the counter pixel electrode12 a-1 were allowed to stand for five minutes without applying anyvoltage. The result indicated that the developed color (magenta) of thefirst electrochromic layer 13 a had been retained, exhibiting excellentimage retaining properties.

In addition, the white reflectance in a dissipation state was measuredfrom the display substrate 11 side using a spectrophotometer LCD-5000(manufactured by Otsuka Electronics). The white reflectance obtained was51%.

[Color Development/Dissipation Test 2]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode was connected to the second drivingconnection portion 11 b′ corresponding to the second display electrode11 b (in the second layer), and the positive electrode was connected tothe counter pixel electrode 12 a-2. A voltage of 4.5 V was then appliedbetween the second display electrode 11 b and the counter pixelelectrode 12 a-2 for one second, which had driven the secondelectrochromic layer 13 b (in the second layer) to develop blue coloraccording to a shape of the counter display electrode 12 a-2 (i.e., lineportion shape). As a result, magenta and blue line portions weredisplayed.

Comparative Example 1 Manufacture of Electrochromic Display Device

A comparative example 1 of the electrochromic display device 110 wasproduced by following a similar method utilized in Example 1 except thatno protective layers were provided in the electrochromic display device110.

[Color Development/Dissipation Test 1]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode and the positive electrode were exchangedsuch that the positive electrode was connected to the first drivingconnection portion 11 a′ corresponding to the first display electrode 11a, and the negative electrode was connected to the counter pixelelectrode 12 a-1. A voltage of −4.5 V was then applied between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for twoseconds, which had driven the first electrochromic layer 13 a (in thefirst layer) to dissipate the developed color (magenta) completely. As aresult, the color of the first electrochromic layer 13 a had returned towhite.

Further, after the application of the voltage of 4.5 V between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for onesecond, the first display electrode 11 a and the counter pixel electrode12 a-1 were allowed to stand for five minutes without applying anyvoltage. The result indicated that the developed color (magenta) of thefirst electrochromic layer 13 a had been retained, exhibiting excellentimage retaining properties.

In addition, the white reflectance in a dissipation state was measuredfrom the display substrate 11 side using a spectrophotometer LCD-5000(manufactured by Otsuka Electronics). The white reflectance obtained was52%.

[Color Development/Dissipation Test 2]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode was connected to the second drivingconnection portion 11 b′ corresponding to the second display electrode11 b (in the second layer), and the positive electrode was connected tothe counter pixel electrode 12 a-2. A voltage of 4.5 V was then appliedbetween the second display electrode 11 b and the counter pixelelectrode 12 a-2 for one second, which had driven the firstelectrochromic layer 13 a (in the first layer) to dissipate the magentacolor developed according to the shape of the counter display electrode12 a-1 (i.e., line portion shape), and also had driven the secondelectrochromic layer 13 b (in the second layer) to develop blue coloraccording to the shape of the counter display electrode 12 a-1 (i.e.,line portion shape) and the counter display electrode 12 a-2 (i.e., lineportion shape). As a result, two blue line portions were displayed.

Comparative Example 2 Manufacture of Electrochromic Display Device

A comparative example 2 of the electrochromic display device 110 wasproduced by following a similar method utilized in Example 1 except thatthe protective layers 15 a to 15 c were formed of a conductive oxide AZO(ZnO+Al₂O₃ (2 wt %)) with the thickness of 10 nm.

[Color Development/Dissipation Test 1]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode and the positive electrode were exchangedsuch that the positive electrode was connected to the first drivingconnection portion 11 a′ corresponding to the first display electrode 11a, and the negative electrode was connected to the counter pixelelectrode 12 a-1. A voltage of −4.5 V was then applied between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for twoseconds, which had driven the first electrochromic layer 13 a (in thefirst layer) to dissipate the developed color (magenta) completely. As aresult, the color of the first electrochromic layer 13 a had returned towhite.

Further, after the application of the voltage of 4.5 V between the firstdisplay electrode 11 a and the counter pixel electrode 12 a-1 for onesecond, the first display electrode 11 a and the counter pixel electrode12 a-1 were allowed to stand for five minutes without applying anyvoltage. The result indicated that the developed color (magenta) of thefirst electrochromic layer 13 a had been retained, exhibiting excellentimage retaining properties.

In addition, the white reflectance in a dissipation state was measuredfrom the display substrate 11 side using a spectrophotometer LCD-5000(manufactured by Otsuka Electronics). The white reflectance obtained was50%.

[Color Development/Dissipation Test 2]

A negative electrode was connected to the first driving connectionportion 11 a′ corresponding to the first display electrode 11 a (in thefirst layer), and a positive electrode was connected to the counterpixel electrode 12 a-1. A voltage of 4.5 V was then applied between thefirst display electrode 11 a and the counter pixel electrode 12 a-1 forone second, which had driven the first electrochromic layer 13 a (in thefirst layer) to develop magenta color according to a shape of thecounter display electrode 12 a-1 (i.e., line portion shape).

Next, the negative electrode was connected to the second drivingconnection portion 11 b′ corresponding to the second display electrode11 b (in the second layer), and the positive electrode was connected tothe counter pixel electrode 12 a-2. A voltage of 4.5 V was then appliedbetween the second display electrode 11 b and the counter pixelelectrode 12 a-2 for one second, which had driven the firstelectrochromic layer 13 a (in the first layer) to dissipate the magentacolor developed according to the shape of the counter display electrode12 a-1 (i.e., line portion shape), and also had driven the secondelectrochromic layer 13 b (in the second layer) to develop blue coloraccording to the shape of the counter display electrode 12 a-1 (i.e.,line portion shape) and the counter display electrode 12 a-2 (i.e., lineportion shape). As a result, two blue line portions were displayed.

Examples 3 and 4 Manufacture of Electrochromic Display Device

Examples 3 and 4 of the electrochromic display device 10 illustrated inFIG. 1 were produced by following a similar method utilized in Example 1except that the protective layers 15 a to 15 c were made of SiO₂ withrespective thicknesses of 0.5 nm (Example 3) and 1 nm (Example 4). Thecolor development/dissipation test 2 was conducted on the examples 3 and4 of the electrochromic display device 10 in a similar manner as thatconducted in Example 1. Note that in the example 3, an additional colordevelopment/dissipation test 2 was conducted on the electrochromicdisplay device 10 by reversing the driving order of the displayelectrodes (i.e., display electrodes 11 a and 11 b) to develop ordissipate color. The results obtained in Examples 1 and 2, andComparative Example Tare summarized in TABLE 1.

TABLE 1 PROTECTIVE DRIVING FILM ORDER DISPLAY THICKNESS (DISPLAY DISPLAYDEVICE (nm) ELECTRODE: DE) RESULT EXAMPLE 1 5 DE 11a → DE 11b DISPLAYED(MAGENTA, BLUE) EXAMPLE 2 10 DE 11a → DE 11b DISPLAYED (MAGENTA, BLUE)EXAMPLE 3 0.5 DE 11a → DE 11b DISPLAYED (MAGENTA, BLUE) EXAMPLE 4 1 DE11a → DE 11b DISPLAYED (MAGENTA, BLUE) EXAMPLE 3 0.5 DE 11b → DE 11a NOTDISPLAYED (BLUE, BLUE) COMPARA- 0 DE 11a → DE 11b NOT TIVE DISPLAYEDEXAMPLE 1 (BLUE, BLUE)

In Examples 3 and 4, a negative electrode was connected to the firstdriving connection portion 11 a′ corresponding to the first displayelectrode 11 a (in the first layer), and a positive electrode wasconnected to the counter pixel electrode 12 a-1. A voltage of 4.5 V wasthen applied between the first display electrode 11 a and the counterpixel electrode 12 a-1 for one second, which had driven the firstelectrochromic layer 13 a (in the first layer) to develop magenta coloraccording to a shape of the counter display electrode 12 a-1 (i.e., lineportion shape) in both Examples 3 and 4.

Subsequently, in Examples 3 and 4, the negative electrode was connectedto the second driving connection portion 11 b′ corresponding to thesecond display electrode 11 b (in the second layer), and the positiveelectrode was connected to the counter pixel electrode 12 a-2. A voltageof 4.5 V was then applied between the second display electrode 11 b andthe counter pixel electrode 12 a-2 for one second, which had driven thesecond electrochromic layer 13 b (in the second layer) to develop bluecolor according to a shape of the counter display electrode 12 a-2(i.e., line portion shape) in both Examples 3 and 4. As a result,magenta and blue line portions were displayed.

Note that in Example 3, the driving order of the display electrodes waschanged (reversed) from the “display electrode 11 a→display electrode 11b” order to the “display electrode 11 b→display electrode 11 a” order.In this case, the negative electrode was initially connected to thesecond driving connection portion 11 b′ corresponding to the seconddisplay electrode 11 b (in the second layer), the positive electrode wasconnected to the counter pixel electrode 12 a-2, and a voltage of 4.5 Vwas then applied between the second display electrode 11 b and thecounter pixel electrode 12 a-2 for one second. The result indicated thatthe second electrochromic layer 13 b (in the second layer) was driven todevelop blue color according to a shape of the counter display electrode12 a-2 (i.e., line portion shape). However, when a negative electrodewas connected to the first driving connection portion 11 a′corresponding to the first display electrode 11 a (in the first layer),a positive electrode was connected to the counter pixel electrode 12a-1, and a voltage of 4.5 V was then applied between the first displayelectrode 11 a and the counter pixel electrode 12 a-1 for one second inExample 3, the result indicated that the first electrochromic layer 13 a(in the first layer) did not develop magenta color according to theshape of the counter display electrode 12 a-1 (i.e., line portionshape), but the second electrochromic layer 13 b (in the second layer)had developed blue color according to a shape of the counter displayelectrode 12 a-2 (i.e., line portion shape). As a result, two blue lineportions were displayed.

According to the above embodiments, there is provided an electrochromicdisplay device having a structure simpler than the electrochromicdisplay device having plural layers of the electrochromic elements, andcapable of independently developing or dissipating desired colors.

So far, the preferred embodiments are described. However, the inventionis not limited to those specifically described embodiments, and variousmodifications and alteration may be made within the scope of theinventions described in the claims.

Embodiments of the present invention have been described heretofore forthe purpose of illustration. The present invention is not limited tothese embodiments, but various variations and modifications may be madewithout departing from the scope of the present invention. The presentinvention should not be interpreted as being limited to the embodimentsthat are described in the specification and illustrated in the drawings.

The present application is based on Japanese priority application No.2010-174192 filed on Aug. 3, 2010, and Japanese priority application No.2011-137121 filed on Jun. 21, 2011, with the Japanese Patent Office, theentire contents of which are hereby incorporated by reference.

1. An electrochromic display device comprising: a display substrate; acounter substrate facing the display substrate; an array of counterelectrodes formed on the counter substrate; at least a first displayelectrode and a second display electrode arranged between the displaysubstrate and the array of the counter electrodes, the first displayelectrode and the second display electrode having a predetermineddistance from each other; a first electrochromic layer arranged on thefirst display electrode and a second electrochromic layer arranged onthe second display electrode; an electrolyte layer arranged between thefirst and the second display electrodes and the array of the counterelectrodes; and a protective layer made of an insulator material formedon a counter electrode facing side surface of one of the first and thesecond display electrodes such that the protective layer is sandwichedbetween the selected one of the first and the second display electrodesand a corresponding one of the first and the second electrochromiclayers.
 2. The electrochromic display device as claimed in claim 1,wherein the insulator material includes a metallic oxide as a majorcomponent.
 3. The electrochromic display device as claimed in claim 1,wherein the protective layer includes a thickness less than a thicknessof the selected one of the first and the second display electrodes onthe counter electrode facing side surface of which the protective layeris formed.
 4. The electrochromic display device as claimed in claim 3,wherein the thickness of the protective layer formed on the counterelectrode facing side surface of the selected one of the first and thesecond display electrodes is in a range of 0.5 to 5 nm.
 5. Theelectrochromic display device as claimed in claim 3, wherein in a casewhere the protective layer is formed on the counter electrode facingside surfaces of both the first and the second display electrodes as afirst protective layer formed on the first display electrode and asecond protective layer formed on the second display electrode, thefirst protective layer and the second protective layer include mutuallydifferent thicknesses.
 6. The electrochromic display device as claimedin claim 1, wherein the insulator material includes one of an Al oxideand a Si oxide.
 7. The electrochromic display device as claimed in claim1, wherein the protective layer is formed by vacuum deposition.
 8. Theelectrochromic display device as claimed in claim 1, wherein voltagesare applied between the first and the second display electrodes and thecorresponding counter electrodes in the order of distance from farthestto closest between the first and the second display electrodes and thecorresponding counter electrodes to subsequently drive the first and thesecond electrochromic layers to develop corresponding colors.